When producing or grading performance of a semiconductor product, test circuits may assist characterization of the product or identification of process variations that may be associated with the semiconductor fabrication. One parameter that may characterize semiconductor products or indicate a variation in process may include the speed of performance.
Test circuits onboard a semiconductor product may be used to characterize certain parameters of semiconductor product. Oscillators may produce a frequency and provide information about the operating speed of a device. But, in order to obtain more precise information about individual elements of the device or the processes of its fabrication to enable isolation of process variations and effects, information regarding the separate rise and fall delay characteristics of the oscillating signal may be needed. As used herein, a rise delay generally refers to the propagation delay through an element or block when receiving a rising edge (low to high transition) at an input. Similarly, a fall delay generally refers to the propagation delay when receiving a falling edge (high to low transition).
The duty cycle of the signal resulting from the oscillator may provide one avenue for such information. However, measurement of the precise duty cycle may be difficult for a variety of reasons. For example, it may be difficult to make a path from the ring oscillator output to the tester input equal for both rising and falling edges across all process variations. Secondly, testers may not have the capabilities for measuring an accurate duty cycle of a clock. Additionally, the output clock from an oscillator might need to be divided in order to make it slow enough for its frequency to be measured by customary testers. Further, such frequency division circuits could be complicated and cumbersome to implement, especially when trying to maintain certain aspects of the original signal.